As a deformed part of an object such as a structure, etc. including a composite material, due to energy, shock, etc., is restored by an elastic force, unlike in an existing metal structure, deformation does not appear outwardly, and the object looks like as being maintained in a normal state. However, defects, such as separation between fine layers inside the object and fine cracks, may occur. When these defects extend or continue to grow during an operation of the structure or a severe load is applied to the object due to the defects, sudden destruction and damage of the object may occur. Thus, for safety of the object, the location of a damaged part needs to be sensed at an initial stage and a proper maintenance is performed so that the object can be restored to its original state.
A technique for monitoring safety of the structure is used as a technique for checking the location of the damaged part and whether the object is damaged. Recently, development for small-sized sensors capable of monitoring the structure through the configuration of a piezoelectric (PZT) sensor and an electrode that receives an electric signal from the PZT sensor by deformation of the PZT sensor has been actively carried out.
For example, Korean Patent Laid-open Publication No. 2012-0083261 as the related art discloses a small sensor capable of monitoring a structure using a PZT sensor and an electrode applied to upper and lower parts of the PZT sensor. The PZT sensor has been regarded as an obstacle to wide utilization, in particular, installation and multi-directional deformation information measurement of the inside of a structure having a large curvature, due to its brittleness caused by a ceramic material. As a result, the utilization range of a sensor having no flexibility with respect to various external forces, such as a fiber Bragg grating (FBG) sensor and the PZT sensor, is very limited in checking and evaluation of soundness of the structure.